Actinic radiation curing jet printing ink

ABSTRACT

Disclosed is an active energy beam curable inkjet printing ink including a pigment, a compound containing two or more ethylenic double bonds, a compound containing one ethylenic double bond and having a molecular weight of 90 to 210, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1 as a first initiator, and acylphosphine oxides as a second initiator. The ink has low viscosity, excellent photo-polymerizability, remarkably excellent curing property, good dispersion stability, causes no dissolution and swelling of ink contacting materials in a printer, and shows excellent discharge stability from nozzles, an excellent adherence property to a recording medium, excellent solvent resistance and water resistance.

FIELD OF THE INVENTION

The present invention relates to an active energy beam curable inkjetprinting ink. More particularly, the present invention relates to anactive energy beam curable inkjet ink which is excellent inphoto-polymerizability, has an excellent curing property and goodstability as an ink, and also causes no dissolution and no swelling ofink-contacting materials in a printer, has an excellent dischargestability from a nozzle, has an excellent adhesion property to recordingmedia, excellent solvent resistance and water resistance.

BACKGROUND OF THE INVENTION

Conventionally, as inkjet inks excellent in water resistance, there arethose obtained by dispersing or dissolving an oil-soluble dye in a highboiling point solvent and those obtained by dissolving an oil-solubledye in a volatile solvent.

As to colorants that have been used, dyes are inferior to pigments invarious kinds of resistance such as light resistance. However, it isgenerally not easy to disperse a pigment stably in an organic solvent,and it is usually difficult to secure a stable dispersibility anddischarging property.

As to ink solvents, an ink using a high boiling point solvent shows nosolvent volatilization on a non-absorbing type recording medium, andmanifests difficult drying through the evaporation of solvents, henceimpossibility of printing onto non-absorbing type substrates. On theother hand, in the case of an ink using a volatile organic solvent, itis possible to form excellent prints even on a non-absorbing substrateby the adhesive property of a resin used and evaporation of solvents.However, since a volatile solvent is the main component of the ink,drying by volatilization of a solvent is very quick on the nozzlesurface of a head, and frequent maintenance is required. Further, asinks are essentially required to be re-soluble in solvents, resistanceto solvents is not sufficiently obtained in some cases.

While there have been such various problems, there is also a utilizationof inks of the type which prevents drying in a head by usingnon-volatile monomers and completes hardening by providing active energyrays. Such inks are disclosed, for example, in Japanese PatentApplication Laid-Open (JP-A) Nos. 62-64874 and 58-32674. These inks aretypically used in printers of continuous type, and particularly, inkshaving a viscosity of 3 to 5 mPa·s are generally used. Since this typeof printer discharges inks continuously, a plurality of volatilesolvents can be used together and in large amounts, and control ofviscosity of the inks and impartment of volatility are relatively easy.

On the other hand, in an on demand mode printer using a piezo element,use of a large amount of volatile solvents increases frequency ofmaintenance and tends to cause a problem of dissolution and swelling ofink contact materials in a printer Also, volatile solvents arerestrained more strictly as a hazardous material defined by the fireprotection law. In the case of an on demand type printer using a piezoelement, an ink having a smaller amount of volatile solvents is thusrequired. However, materials used in an active energy beam curable inkhave been had relatively high viscosity. Inks having so low viscosity asto enable discharge also in a conventional type printer, an excellentcuring property, and excellent stability, have not been obtained untilnow.

One object of the present invention is to provide an active energy beamcurable inkjet ink having low viscosity, excellentphoto-polymerizability, excellent curing property, and good stability.

Another object of the present invention is to provide an active energybeam curable inkjet ink causing no dissolution and swelling of inkcontact materials in a printer, and showing excellent dischargestability from nozzles, excellent adherence to a recording medium, andexcellent solvent resistance and water resistance.

SUMMARY OF THE INVENTION

The present invention is an active energy beam curable inkjet printingink comprising a pigment, a compound containing two or more ethylenicdouble bonds, a compound containing one ethylenic double bond and havinga molecular weight of 90 to 210,2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1 as a firstinitiator, and acylphosphine oxides as a second initiator.

In the present invention, it is preferable that the compound containingone ethylenic double bond is 2-phenoxyethyl acrylate. It is preferablethat the inkjet printing ink further comprises a pigment dispersingagent. It is preferable that the inkjet printing ink does not contain anon-reactive solvent. The pigment contained in the inkjet printing inkof the present invention is preferably in the form of pigment particleshaving an average particle size of 10 to 150 nm. The inkjet printing inkaccording to the present invention has preferably a viscosity at 25° C.of 5 to 50 mPa·s.

The inkjet printing ink of the present invention is an ink obtained bydispersing a pigment in an active energy ray-hardening compound. Theinkjet printing ink has low viscosity, causes no dissolution andswelling of ink contact materials in a printer, and has excellentphoto-polymerizability, very good curing property and excellentdispersion stability. It also shows very good discharge stability fromnozzles. When inkjet recording/printing is conducted using the ink ofthe present invention, a recorded material showing high transparency andhaving excellent gloss and various resistive properties can be obtained.

DETAILED DESCRIPTION OF THE INVENTION

As a pigment contained in the inkjet ink of the present invention,achromatic pigments such as carbon black, titanium oxide, and calciumcarbonate or chromatic organic pigments may be used. Examples of theorganic pigment include insoluble azo pigments such as toluidine red,toluidine maroon, hansa yellow, benzidine yellow, and pyrazolone red,soluble azo pigments such as lithol red, helio bordeaux, pigmentscarlet, and permanent red 2B, derivatives from vat dyes such asalizarin, indanthrone, and thioindigo maroon, phthalocyanine-typeorganic pigments such as phthalocyanine blue and phthalocyanine green,quinacridone-type organic pigments such as quinacridone red andquinacridone magenta, perylene-type organic pigments such as perylenered and perylene scarlet, isoindolinone-based organic pigments such asisoindolinone yellow and isoindolinone orange, pyranethrone-type organicpigments such as pyranethrone red and pyranethrone orange,thioindigo-type organic pigments, condensed azo-type organic pigments,benzimidazolone-type organic pigments, quinophthalone-type organicpigments such as quinophthalone yellow, isoindoline-type organicpigments such as isoondoline yellow, and other pigments such asfravanethrone yellow, acylamide yellow, nickel azo yellow, copper azomethine yellow, perynone orange, anthrone orange, dianthraquinonyl red,and dioxazine violet.

Using color index (C.I.) numbers, examples of the organic pigmentsinclude C.I. Pigment Yellow 12, 13, 14, 17, 20, 24, 74, 83, 86, 93, 109,110, 117, 125, 128, 129, 137, 138, 139, 147, 148, 150, 151, 153, 154,155, 166, 168, 180, 185, C.I. Pigment Orange 16, 36, 43, 51, 55, 59, 61,C.I. Pigment Red 9, 48, 49, 52, 53, 57, 97, 122, 123, 149, 168, 177,180, 192, 202, 206, 215, 216, 217, 220, 223, 224, 226, 227, 228, 238,240, C.I. Pigment Violet 19, 23, 29, 30, 37, 40, 50, C.I. Pigment Blue15, 15:1, 15:3, 15:4, 15:6, 22, 60, 64, C.I. Pigment Green 7, 36, andC.I. Pigment Brown 23, 25, 26.

Among the above-mentioned pigments, quinacridone-type organic pigments,phthalocyanin-type organic pigments, benzimidazolone-type organicpigments, isoindolinone-type organic pigments, condensed azo-typeorganic pigments, quinophthalone-type organic pigments, isoindoline-typeorganic pigments and the like are preferable because of their excellentlight resistance.

The organic pigment is preferably a fine pigment having an averageparticle size of 10 to 150 nm in terms of measured values by laserscattering. When the pigment has an average particle size of less than10 nm, the light resistance will be lowered due to the decrease inparticle size. When, on the contrary, over 150 nm, stable maintenance ofdispersion becomes difficult and precipitation of the pigment tends tooccur.

Fine organic pigment production can be conducted, for example, accordingto the following method. That is, a mixture composed of at least threecomponents, an organic pigment, a water-soluble inorganic salt in anamount three times or more by weight that of the organic pigment, and awater-soluble solvent is prepared as a clay-like mixture, and themixture is strongly kneaded by a kneader and the like so as to be finedbefore charging into water. The mixture is then stirred by a high speedmixer and the like to give a slurry. Then, filtration and water-washingof the slurry are repeated, to remove the water-soluble inorganic saltand the water-soluble solvent. In the fine particle production process,resins, pigment dispersing agents and the like may be added.

Examples of the water-soluble inorganic salt include sodium chloride andpotassium chloride. These inorganic salts are used in an amount of 3times weight or more, and preferably 20 times weight or less of theorganic pigment. When the amount of the inorganic salt is less than 3times weight, a treated pigment having a desired size is not obtained.When it is over 20 times weight, washing treatment in a subsequentprocess will be enormous, and the substantial treated amount of theorganic pigment decreases.

The water-soluble solvent is used to make suitable clay-like conditionof the organic pigment and the water-soluble inorganic salt used as amilling aid, and to efficiently conduct sufficient milling, and is notparticularly restricted providing it is a solvent soluble in water.However, a solvent having a high boiling point of 120 to 250° C. ispreferable from the standpoint of safety since in kneading, thetemperature increases and the solvent manifests a condition of easyevaporation. Examples of the water-soluble solvent include2-(methoxymethoxy)ethanol, 2-butoxyethanol, 2-(isopentyloxy)ethanol,2-(hexyloxy)ethanol, diethylene glycol, diethylene glycol monomethylether, diethylene glycol monoethyl ether, diethylene glycol monobutylether, triethylene glycol, triethylene glycol monomethyl ether, liquidpolyethylene glycol, 1-methoxy-2-propanol, 1-ethoxy-2-propanol,dipropylene glycol, dipropylene glycol monomethyl ether, dipropyleneglycol monoethyl ether and lower molecular weight polypropylene glycol.

In the present invention, it is preferable that a pigment is containedin an amount of 3 to 15% by weight in the inkjet ink in order to obtaina sufficient concentration and sufficient light resistance.

Examples of a compound which contains two or more ethylenicallyunsaturated double bonds include those referred to as prepolymers,oligomers and the like. Specific examples include ethylene glycoldi(meth)acrylate, diethylene glycol di(meth)acrylate, polyethyleneglycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, ethoxylated1,6-hexanediol diacrylate, neopentyl glycol di(meth)acrylate,ethoxylated neopentyl glycol di(meth)acrylate, propoxylated neopentylglycol di(meth)acrylate, tripropylene glycol di(meth)acrylate,polypropylene glycol diacrylate, 1,4-butanediol di(meth)acrylate,1,9-nonanediol diacrylate, tetraethylene glycol diacrylate,2-n-butyl-2-ethyl-1,3-propanediol diacrylate, dimethylol tricyclodecanediacryalte, hydroxypivalic neopentyl glycol diacrylate, 1,3-butyleneglycol di(meth)acrylate, ethoxylated bisphenol A di(meth)acrylate,propoxylated bisphenol A di(meth)acrylate, cyclohexane dimethanoldi(meth)acrylate, dimethylol dicyclopentane diacrylate,trimethylolpropane triacrylate, ethoxylated trimethylolpropanetriacrylate, propoxylated trimethylolpropane triacrylate,pentaerythritol triacrylate, tetramethylolpropane triacrylate,tetramethylolmethane triacrylate, pentaerythritol tetraacrylate,caprolactone-modified trimethylolpropane triacrylate, ethoxylatedisocyanuric triacrylate, tri(2-hydroxyethyl isocyanurate) triacrylate,propoxylate glyceryl triacrylate, tetramethylolmethane tetraacrylate,pentaerythritol tetraacrylate, ditrimethylolpropane tetraacrylate,ethoxylated pentaerythritol tetraacrylate, dipentaerythritolhexaacrylate, neopentyl glycol oligo acrylate, 1,4-butanediol oligoacrylate, 1,6-hexanediol oligo acrylate, trimethylolpropane oligoacrylate, pentaerythritol oligo acrylate, urethane acrylate, epoxyacrylate and polyester acrylate. These compounds may be used singly orin combination of two or more if necessary.

These compounds, which contain two or more ethylenic double bonds, areused preferably in an amount of 15 to 60% by weight in the ink, since insuch an amount the curing speed and the cross-linking concentration willbe high and the water resistance, hardness, and gloss are improved.

As a compound containing one ethylenic double bond, that is to becontained in the inkjet ink, those having a molecular weight of 90 to210 are excellent in photo-polymerizability, show a good curing propertyand excellent stability, and cause no problems such as dissolution andswelling of ink-contacting materials in a printer. When the molecularweight is less than 90, stability is poor though the curing property isexcellent, and dissolution and swelling of ink-contacting materialsoccur in a printer. Also, among such compounds, those harmful to humanbodies and likely to cause cancer are included. Contrary, when themolecular weigh is over 210, problems like dissolution and swelling ofink contacting materials in a printer will not be caused, and stabilityis excellent. Yet, curing properties will be quite inferior though.

Examples of the compound containing one ethylenic double bond and havinga molecular weight of 90 to 210 include 2-phenoxyethyl acrylate,acryloyl morpholine, N-vinyl caprolactam, 2-hydroxyethyl acrylate,2-hydroxypropyl acrylate, 4-hydroxybutyl acrylate, isobutyl acrylate,t-butyl acrylate, isooctyl acrylate, isobonyl acrylate, cyclohexylacrylate, 2-methoxyethyl acrylate, methoxytriethylene glycol acrylate,2-ethoxyethyl acrylate, tetrahydrofurfuryl acrylate, 3-methoxybutylacrylate, benzyl acrylate, ethoxyethoxyethyl acrylate, butoxyethylacrylate, ethoxydiethylene glycol acrylate, methoxydipropylene glycolacrylate, methylphenoxyethyl acrylate and dipropylene glycol acrylate.

These compounds containing one ethylenic double bond and having amolecular weight of 90 to 210 may be used singly or in combination oftwo or more. Particularly among them, 2-phenoxyethyl acrylate can bepreferably used. It is preferable that the amount of these compoundsused in an ink is from 20% to 75% by weight. When the amount is lessthan 20% by weight, the viscosity of the ink will increase, and willmake the discharge from an inkjet printer impossible. The durability ofprinted matters will deteriorate when the amount exceeds 75% by weight.

Preferable as the photo-polymerization initiator according to thepresent invention are those easily absorbing peak wavelength lightsbetween 300 nm to 450 nm emitted mainly from an ultraviolet lamp or anultraviolet laser, those showing excellent compatibility with aphoto-polymerizable compound, and photo-chemically, those having aquantum efficiency near 1. Further, for enhancing photo-polymerizationinitiation efficiency, a photo-polymerization promoter may be used incombination. The present inventors have found that high sensitivity isobtained when a photo-polymerization initiator is combined with2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1 andacylphosphine oxides. The reason for this is hypothesized that whenirradiated with an activation light beam, the latter is self dissociatedefficiently, and produces radicals, due to the energy or electronstransferred from the former.

In general, when the addition amount of a photo-polymerization initiatorincreases, a curing property becomes more excellent, while the viscosityof the ink increases. Therefore, in the case of active energy beamcurable ink jet inks, an initiator giving expectancy of the effect witha small amount addition has conventionally been desired. Since thephoto-polymerization initiator component of the present invention,2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1 has arelatively high molecule absorption coefficient, it easily absorbsactive ray even if carbon black tending to disturb light transmittancein a photo-sensitive layer is present. Further, since the maximumabsorption wavelength (λ_(max)) is around 365 nm, the sensitivity ishigh because of the coincidence with the peak wavelength of lights suchas those of an ultraviolet lamp. Therefore, a sufficient effect can beobtained with a small addition amount. It is preferable that thisinitiator is used in an amount of 0.1 to 5% by weight in the ink.Examples of the acylphosphine oxide include2,4,6-trimethylbenzoyldiphenylphosphine oxide andbis(2,4,6-trimethylbenzoyl)acylphosphine oxide. Particularly,bis(2,4,6-trimethylbenzoyl)acylphosphine oxide can be mentioned. It ispreferable that it is used in an ink in an amount of 5 to 10% by weight.With the constitution of single use of these photo-polymerizationinitiators, a sufficient curing property cannot be obtained, andresultantly, the use amount of an expensive photo-polymerizationinitiator increases, to cause increase in the viscosity of the ink,being economically undesirable.

As the photo-polymerization promoter, for example, ethylp-dimethylaminobenzoate, 4,4′-dimethylaminobenzophenone, and4,4′-diethylaminobenzophenone are listed. These photo-polymerizationpromoters can be used singly or in combination of two or more.

In the ink jet ink of the present invention, it is preferable tocompound an aromatic derivative such as hydroquinone, p-methoxyphenol,t-butyl catechol, pyrogallol and the like in an amount of 0.01 to 5% byweight in an ink, for enhancing stability with time of the ink andstability on machine in a printing device.

As the pigment dispersing agent of the present invention, for example,hydroxyl group-containing carboxylates, salts of long chainpolyaminoamides with high molecular weight acid esters, salts of highmolecular weight polycarboxylic acids, salts of long chainpolyaminoamides with polar acid esters, high molecular weightunsaturated acid esters, high molecular weight copolymers, modifiedpolyurethanes, modified polyacrylates, polyether ester type anionicactivating agents, naphthalenesulfonic acid formalin condensate salts,aromatic sulfonic acid formalin condensate salts, polyoxyethylenealkylphosphates, polyoxyethylene nonylphenyl ethers, stearylamine acetate andpigment derivatives are listed.

Specific examples of the pigment dispersing agent include: Anti-Terra-U(polyaminoamide phosphoric acid salt) made by BYK Chemie;Anti-Terra-203/204 (high molecular weight polycarboxylic acid salt);Disperbyk-101 (polyaminoamide phosphoric acid salt and acid ester), 107(hydroxyl group-containing carboxylate), 110 (copolymer containing acidgroup), 130 (polyamide), 161, 162, 163, 164, 165, 166, and 170 (highmolecular weight copolymer); 400; Bykumen (high molecular weightunsaturated acid ester); BYK-P104 and P105 (high molecular weightunsaturated polycarboxylic acid); P104A and 240S (high molecular weightunsaturated polycarboxylic acid and silicone-based substance); and,Lactimon (long chain amine and unsaturated polycarboxylic acid andsilicone).

Other examples thereof include: Efka 44, 46, 47, 48, 49, 54, 63, 64, 65,66, 71, 701, 764 and 766 made by Efka CHEMICALS; Efka Polymer 100(modified polyacrylate), 150 (aliphatic modified polymer), 400, 401,402, 403, 450, 451, 452, 453 (modified polyacrylate) and 745 (copperphthalocyanine-based); Florene TG-710 (urethane oligomer) made byKYOEISHA CHEMICAL CO. LTD; Flonone SH-290 and SP-1000; “Polyflow No.50E, No. 300 (acrylic copolymer); Disperon KS-860, 873SN, 874 (highmolecular weight dispersing agent), #2150 (aliphatic poly-valentcarboxylic acid) and #7004 (polyether ester type) made by KUSUMOTOCHEMICALS LTD.

Further examples thereof include: Demol RN, N (naphthalenesulfonic acidformalin condensate sodium salt), MS, C, SN-B (aromatic sulfonic acidformalin condensate sodium salt), and EP, made by Kao Corp.; HomogenolL-18 (polycarboxylic acid type polymer), Emargen 920, 930, 931, 935,950, 985 (polyoxyethylene nonylphenyl ether), Acetamine 24 (coconutamine acetate), and 86 (stearylamine acetate); Solsperse 5000(phthalocyanine ammonium salt-based), 13240, 13940(polyesteramine-based), 17000 (fatty acid amine-based), 24000, and32000, made by Zeneka; Nikol T106 (polyoxyethylene sorbitanemonooleate), MYS-IEX (polyoxyethylene monostearate), and Hexagline 4-0(hexaglyceryl tetraoleate) made by Nikko Chemicals Co. LTD.

A pigment dispersing agent is preferably contained in an amount of 0.1to 10% by weight in the ink.

The inkjet ink of the present invention is produced, for example, bysufficiently dispersing a pigment together with an active energybeam-curing compound and a pigment dispersing agent by using a usualdispersing machine such as a sand mill. It is preferable that aconcentrate having a high pigment concentration is previously producedand diluted with an active energy beam curable compound. Sincesufficient dispersion is possible by using a usual dispersing machine,it does not take any extra energy and duration for the dispersionprocess. Consequently, it is not likely to cause any modifications inthe ink components during the dispersion and an ink which has excellentstability is obtained. It is preferable that the ink is filtratedthrough a filter having a pore diameter of 3 μm or less, furtherpreferably 1 μm or less.

It is preferable that the viscosity at 25° C. of the inkjet inkaccording to the present invention is controlled at as high as 5 to 50mPa·s. An ink with a viscosity at 25° C. of 5 to 50 mPa·s shows a stabledischarge property particularly on a head of a usual frequency of 4 to10 kHz and even on a head of a high frequency of 10 to 50 kHz.

When an ink with a viscosity of less than 5 mPa·s is used, a well-timedoperation of discharge will be deteriorated. When an ink with aviscosity of over 50 mPa·s is used, a discharge itself will be weakenedeven if some mechanism which lowers the viscosity by heating isincorporated in the head, and the discharge stability may deteriorate,leading to no discharge at all.

It is preferable that the inkjet ink of the present invention is an inkwhich gives a conductivity of 10 μS/cm or less in a piezo head and showsno electric corrosion in the head. In a continuous type, it is necessaryto control the conductivity by an electrolyte, and in this case it isnecessary to control the conductivity to 0.5 mS/cm or more.

In order to utilize an inkjet ink of the present invention, first it isfed to a printer head of an inkjet recording type printer, and isdischarged from the printer head onto a substrate. Then, an irradiationwith active energy rays such as ultraviolet rays and electron beams isconducted. By the irradiation, the composition on a printing medium ishardened quickly.

As a source of active energy rays, in the case of irradiation withultraviolet rays, for example a high pressure mercury lamp, metal halidelamp, low pressure mercury lamp, ultra-high pressure mercury lamp,ultraviolet laser or sunlight may be used. When hardening is conductedwith electron beams, it is usually effected with an electron beam havingan energy of 300 eV or less. However, it is also possible to effecthardening instantly with an irradiation amount of 1 to 5 M rad.

EXAMPLES

The present invention will be further illustrated in detail below basedon examples. Parts and % in the examples are parts by weight and % byweight, respectively.

A pigment, a dispersing agent and a monomer shown in Table 1 werecharged together in a sand mill and dispersed for 4 hours, to obtainactive energy beam curable IJ ink raw liquid. Next, an initiator wasadded to the ink raw liquid, and mixed gently until dissolution of theinitiator. Then, it was filtrated under pressure through a membranefilter to obtain an active energy beam curable IJ ink.

Printing was conducted on various substrates (polycarbonate,polystyrene, ABS (acetonitrile-styrene-butadiene copolymer), polyvinylchloride, polyethylene teraphthalate, and polybutylene terephthalate)using thus obtained inks by an IJ printer having a piezo head. Then,hardening of a printed body was conducted under a condition of atransfer speed of 10 meter per minute by using a UV irradiationapparatus (one metal halide lamp, out put 120 W).

TABLE 1 Example No. 1 2 3 4 5 6 7 8 Pigment P1 5 5 P2 5 5 P3 5 5 P4 5 5Mono- PEA Molecular 60 45 60 60 50 mer weight: 192 ACMO 141 45 45 IBXA208 45 TMPTA 296 35 35 35 20 NPGDA 212 50 50 HDDA 226 50 50 25 Dis-13940 3 3 persing 24000 3 3 agent  5000 1.5 1.5 22000 1.5 1.5 1.5 1.5L-18 3 3 Efka 49 4.5 4.5 Initiator  369 3 4 3 4 3 4 5 5  819 5 5 5 5 TPO5 5 5 5 Numerical values indicate parts.

Pigments, monomers, dispersing agents, and initiators in Table 1 are asfollows, respectively:

Pigment

Pigment P1

250 parts of crude copper phthalocyanine (“Copper Phthalocyanine”manufactured by Toyo Ink MFG. CO. LTD.), 2500 parts of sodium chlorideand 160 parts of polyethylene glycol (“Polyethylene Glycol 300”,manufactured by Tokyo Kasei K.K.) were charged in a stainless 1 gallonkneader (manufactured by Inoue Manufacturing Co. LTD.), and kneaded for3 hours. Then, the mixture was added into 2.5 liter hot water, andstirred for about 1 hour by a high speed mixer while heating at about80° C. to give a slurry. Next, filtration and water-washing wererepeated 5 times to remove sodium chloride and solvents. Then, theslurry was subjected to spray drying to obtain a dry, treated pigmentP1.

Pigment P2

250 parts of a quinacridone-type red pigment (“Cinquasia MagentRT-355-D”, manufactured by Ciba Geigy), 2500 parts of sodium chlorideand 160 parts of “Polyethylene Glycol 300” were charged in a stainless 1gallon kneader, and the same procedure was effected as for Pigment P1 toobtain a treated pigment P2.

Pigment P3

250 parts of a benzimidazolone-type yellow pigment (“Hostaperm YellowH3G”, manufactured by Hoechst), 2500 parts of sodium chloride and 160parts of “Polyethylene Glycol 300” were charged in a stainless 1 gallonkneader, and the same procedure was effected as for Pigment P1 to obtaina treated pigment P3.

Pigment P4

A carbon black pigment “Printex 150T” (manufactured by Degussa) was usedas Pigment P4.

Monomer

-   “PEA”: 2-phenoxyethyl acrylate (Viscoat #192, manufactured by OSAKA    ORGANIC CHEMICAL INDUSTRY LTD.)-   “ACMO”: acryloylmorpholine (ACMO, manufactured by KOHJIN Co. Ltd.)-   “IBXA”: isobonyl acrylate (IBXA, manufactured by OSAKA ORGANIC    CHEMICAL INDUSTRY LTD.)-   “TMPTA”: trimethylolpropane triacrylate (KS-TMPTA, manufactured by    Nippon Kayaku Co., Ltd.)-   “NPGDA”: neopentyl glycol diacrylate (KAYARAD MANDA, manufactured by    Nippon Kayaku Co., Ltd.)-   “HDDA”: 1,6-hexanediol diacrylate (KS-HDDA, manufactured by Nippon    Kayaku Co., Ltd.)

Dispersing Agent

-   “13940”: polyester amine-based dispersing agent (“Solsperse 13940”,    manufactured by Zeneka)-   “24000”: aliphatic modified dispersing agent (“Solsperse 24000”,    manufactured by Zeneka)-   “5000”: blue pigment dispersing agent (“Solsperse 5000”,    manufactured by Zeneka)-   “22000”: yellow pigment dispersing agent (“Solsperse 22000”,    manufactured by Zeneka)-   “L-18”: polycarboxylic acid type polymer dispersing agent    (“Homogenol L-18”, manufactured by Kao Corp.)-   “Efka”49; modified polyacrylate-based dispersing agent (“Efka 49”,    manufactured by Efka CHEMICAL)

Initiator

-   “369”: 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1    (“Irgacure 369”, manufactured by Ciba Speciality Chemicals)-   “TPO”: 2,4,6-trimethylbenzoyl diphenylphosphine oxide (“Lucirine    TPO”, manufactured by BASF)-   “819”: bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide (“Irgacure    819”, manufactured by Ciba Speciality Chemicals)

COMPARATIVE EXAMPLES

A pigment, a dispersing agent and a monomer shown in Table 2 werecharged together in a sand mill and dispersed for 4 hours, to obtain anactive energy beam curable IJ ink raw liquid. Next, a photo initiator isadded to the ink raw liquid, and mixed gently until dissolution of thephoto initiator. Then, this was filtrated under pressure through amembrane filter to obtain an active energy beam curable IJ ink. Printingwas conducted on the substrate above-mentioned using thus obtained inkby an IJ printer having a piezo head. Then, hardening of a printed bodywas conducted under a condition of a transfer speed of 10 meter perminute by a UV irradiation apparatus (a metal halide lamp: out put 120W).

TABLE 2 Comparative Example No. 1 2 3 4 5 6 7 8 Pigment P1 5 5 5 5 P4 55 5 5 Monomer/ PEA Molecular 60 60 60 60 Pre- weight: 192 polymer NVF 71 45 45 LA 240 60 60 TMPTA 296 35 35 50 35 35 35 50 35 Dispersing13940 3 3 3 3 agent  5000 1.5 1.5 1.5 1.5 Efka 49 4.5 4.5 4.5 4.5Initiator  369 5 3 3 5 3 3  819 7 5 5 7 5 5  651 5 5 Numerical valuesindicate parts.

Components in Table 2 are as follows:

Pigment

Pigments P1 and P2 in Table 2 were the same compounds as in Examples 1to 8.

Dispersing Agent

These are as already described.

Initiator

“651” is 2,2-dimethoxy-1,2-diphenylethane-1-one (“Irgacure 651”,manufactured by Ciba Speciality Chemicals). Initiators “369” and “819”are as already described.

Monomer

“NVF” is N-vinylformamide (“Beam Set 770”, manufactured by ArakawaChemical Industries LTD.). “LA” is lauryl acrylate (“NK Ester LA”,manufactured by Shin-Nakamura Chemical Co. LTD.). Other monomers are asalready described.

Inks and printed materials obtained in Examples 1 to 8 and ComparativeExamples 1 to 8 were evaluated on the following items. The results areshown in Table 3.

Viscosity

Viscosity of inks was measured at 25° C. using a B type viscometer. Theunit of viscosity is “mPa·s” in Table 3.

Curing Property

Curing properties of inks were quantified by pass numbers required witha UV irradiation apparatus before their tack by finger touch was lost.

Stability with a Lapse of Time

Dispersed conditions of inks after storage for 1 month at 25° C. wereevaluated visually and by the measurement of any change in viscosity.

◯; Precipitations were not observed, nor the change in viscosity.

Δ: Precipitations were not observed; yet some increase in viscosity wasobserved.

x: Precipitations were observed.

Stability with Member Materials

Inks were placed on various substrates, and their conditions after lefta whole day and night were observed.

⊚; No corrosion was observed in any substrate.

◯; Corrosion was observed in one or two types of substrate.

x: Corrosion was observed in almost all substrates.

TABLE 3 Results of Evaluations Suitability Stability with Curing with amember No. Viscosity property lapse of time materials Example 1 34.5 1 OO 2 30.2 1 O O 3 18.6 1 O O 4 18.2 1 O O 5 33.6 1 O O 6 22.5 1 O O 733.2 1 O O 8 32.8 1 O O Comparative 36.7 3 O O Example 1 2 34.1 3 O O 321.3 1 Δ X 4 30.2 Not O ⊚ hardened 5 35.9 5 O O 6 33.5 5 O O 7 22.0 1 ΔX 8 30.8 Not O ⊚ hardened

1. An active energy beam curable inkjet printing ink comprising apigment, a compound containing two or more ethylenic double bonds, acompound containing one ethylenic double bond and having a molecularweight of 90 to 210,2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butanone-1 as a firstinitiator, and acylphosphine oxides as a second initiator.
 2. The inkjetprinting ink according to claim 1, wherein the compound containing oneethylenic double bond is 2-phenoxyethyl acrylate.
 3. The inkjet printingink according to claim 1, further comprising a pigment dispersing agent.4. The inkjet printing ink according to claim 1, wherein pigment is inthe form of pigment particles having an average particle size of 10 to150 nm.
 5. The ink jet printing ink according to claim 1, wherein theinkjet printing ink has a viscosity of 5 to 50 mPa·s at 250° C.
 6. Aprocess, comprising: inkjet printing the inkjet printing ink accordingto claim 1 onto a plastic surface, and hardening the printed surfacewith UV irradiation.